To examine the effect of polishing and glazing by numerous operators on the biaxial flexure strength of different dental CAD/CAM glass-ceramics
Method:
Over a 2-year period, three types of CAD/CAM glass ceramic blocks [Vita Mark II (a feldspathic glass-ceramic, Vident), EmpressCAD, (a leucite glass-ceramic) and e.maxCAD (a lithium-disilicate glass-ceramic)] were milled into biaxial flexure discs (1.2±0.1mm thickness by 14.0±0.1mm diameter) in accordance with ISO6872 using the Cerec MCXL CAD/CAM system. The specimens where de-sprued and then treated one of three ways by over 120 different operators: no treatment(milled), polished using the Optrafine polishing system or glazed with the corresponding material glaze. This produced 8 material/surface treatment groups (N=24): Group 1:Vita/Milled, Group 2: EmpressCAD/Milled, Group 3: Vita/Polished, Group 4: EmpressCAD/Polished, Group 5: Vita/Glazed, Group 6: EmpressCAD/Glazed, Group 7: e.maxCAD/blue state, and Group 8:e.maxCAD/Glazed. The specimens were then measured for thickness individually and loaded in a pin-on-three-ball biaxial loading fixture until failure using an Intron Universal testing machine.
Result:
Biaxial flexure strengths (Mean±SD) groups are listed below. One-way univariate analysis of variance (ANOVA) indicated a significant difference in biaxial flexure strength, p<0.05. Follow up multiple comparisons (Tukey HSD) indicated significantly higher strength for Group 8 than all other groups. Group 6 was found to be significantly higher than Groups 1-5, but not Group 7 which was not different than Groups 5 or 6. There was no significant difference in bond strength between Groups 1-5.
Groups Number |
Biaxial Flexure Strength (MPa) |
3 |
125.9±25.1A |
1 |
128.0±25.1A |
4 |
143.4±19.0A |
2 |
146.1±23.9A |
5 |
152.9±29.1A,B |
7 |
186.5±25.6B,C |
6 |
215.2±41.1C |
8 |
441.7±87.1D |
Conclusion:
Within the bounds of this study, glazing produced statistically higher biaxial flexure strengths of the leucite glass-ceramic over the milled or polished conditions, while glazed lithium disilicate was higher than all other tested groups produced by multiple operators over a 2-year period.